Those drivers are written associated with specific products. For example
http://www.nvidia.com/object/macosx-313.01.02f01-driver.html
on the supported products tab is:
GTX 680 for Mac
GTX 285 for Mac
GT 120
8800 GT
K5000 for Mac, 4000 for Mac
FX 5600, FX 4800 for Mac
Those are all products that went to market for sale. For example, updates in 10.8.3 arrived around the same time as
https://www.macrumors.com/2013/04/0...tx-680-mac-edition-graphics-card-for-mac-pro/
Coincidence?
If there is no card vendor asking them and Apple isn't asking them then there is little to no demand allocate development resources this to cover a broad spectrum of new cards and implementations.
Nvidia has multiple implementation per major architecture rollout. A GK110 is not a GK104
The normal driver distribution path for embedded Mac graphics is through Apple.
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Goes back to #1. If limited demand has killed off 3rd card vendor interest then where's Nvidia's motivation? What has typically happened is one vendor takes a stab (recently EVGA) and then firmware and drivers go rogue. This results in the numbers sold and margin is so small (have to use discounts to move the cards) the Apple store doesn't want to bother to stock them.
if there was a demand problem of cards priced "too high" before moving them to a external PCIe enclosure isn't going to make them any more cost effective.
Your argument has multiple holes in it. There is still no "official" GK110 card for Macs yet the drivers have existed IN THE DRIVERS AS PART OF OS well back into Mt. Lion. (Was a front page news story here when I found them)
So if Apple only supports existing cards, why does every Mac on the planet running 10.8.2 or later have all of the files needed to run a Titan? There is a kid in Malaysia with a MacBook Air and on his hard drive are Titan drivers. In every DP of 10.9 have been Titan drivers with OpenCl.
Starting in 10.7 there were drivers for GF110 (GTX570/580) while there were never ANY cards from that family on Apple store. So Apple could have made the cards not work but instead the drivers were distributed BY Apple.
Second major flaw in your argument is that the 3rd party cards stopped employing means of flash blocking. The Radeon 9800 and 3870 used different sized EEPROMs and had tiny resistors moved to block home flashing.
The 5770 and 5870 had a block in EFI. (Netkas figured this out)
8800gt, Gtx285 and ALL of the Quadro cards you listed used the "file too big/EEPROM too small" method. Quadro cards additionally employed a "PC cards have different ports than Mac" which makes flashed cards wonky and ill matched. 4800 even uses different fan controller making flashed cards roar like Niagara.
Then all of a sudden when 7950 and GTX680 come out, NOTHING was done to discourage flashing. So instead of skilled soldering work standing in the way, anyone at home can flash those cards. Sapphire went to trouble of making whole new fan and moving a resistor to restrict PCIE speed but NOTHING was done to actually slow home flashing. They even made fixing PCIE speed a matter of REMOVING a tiny resistor, something more people can do than sourcing and ADDING a tiny SM 10k ohm resistor, as was case on 3870. Non essential to flashing, AND easier. Both EVGA and Sapphire could have easily done something, no attempt was made. So just like Radeon 8500, home flashing by end user is far more common.
Mind you, they did go to the bother of the EEPROM too small trick on K5000. As if they gave 680 as a freebie but held back K5000.
Anyhow, something changed. No attempt made to slow flashing hasn't been case since Radeon 8500, and both cards came out at same time. (680 & 7950)
Someone, somewhere decided not to even try. And before you say that these blocks would only be symbolic, let me say that the 3870 remained unflashable for some time, many months after intro you bought a Sapphire one or you didn't have a working card. Took us quite some time to find the pesky little resistor. So 0 (ZERO) people flashing at home for more than a year after intro.
So Sapphire had to know that leaving door wide open on 7950 would lead to more cards flashed in wild. They did nothing to stop or even slow this.
Many people could have tightened the Mac GPU market by making drivers more specifically targeted to ONLY official cards, instead Apple servers hand out drivers for MOST cards. EVGA and Sapphire could have kept flashing to a minimum during first 6 months of release with any of the tricks they used before, they didn't even try.
I have seen this as "hey, look, we wrote a bunch of drivers for cards nobody wants to bother selling, anyone interested?"